Hydrodealkylation of hydrocarbons



borundum,

United. .States Parent" 2,924,555) HYDRODEALKYLATION oF HYnRocARBoNsArmand M. Souby, Chambers County, Tex., assignor, by mesne assignments,to Esso Research and Engineering Company, Elizabeth, NJ., a corporationof Delaware Application August 1, 1956, Serial No. 601,556

8 Claims. (Cl. 208-107) The present invention is directed to a method'for dea'lkylating alkylated aromatic hydrocarbons. More particularly,the invention is directed'to vthe`thermaldealkylatin of alkylated:aromatic hydrocarbons. In its r'nore'speciic aspects, theinvention isdirected to the thermal dealkylation of alkylated aromatic hydrocarbonsatan elevated temperature in the presence. of hydrogen. .The presentinvention may'bebrieiiy` describedxas a method for thermallydealkylatin'g. analkylated aromatic hydrocarbonin `which the formationof coke is controlled and suppressed. .1' l z i The alkylated aromatichydrocarbon feed is heated in athermal dealkylation zone in the presenceof hydrogen to a temperature withinthe'range betweenA about 1l00 andabout 1600 F. and at a pressure within the range between about-400 and4about 1000 pounds per square inch gauge for a time within the range `ofabout 2 and about 120 seconds in the presence of a-uidized bed ofcatalytically' inert :linelyfdivided solids in vwhich a liquid productand a residue-gas are produced. .In the present invention theresidue gasis flowedthrough a sensing zone to obtain a signal `which `is a functionof the methane to hydrogen ratio in the*residue gas."This Asignalis-then employed to vary the ratioof hydrogen and alkylated aromatichydrocarbon feed in the thermal reaction zone to provide a methane tolhydrogen ratio in the residue gas such that 'the ratiofof theequilibrium methane concentration to the actual methane concentration isabove about 1.7 times the thermodynamic equilibrium ratio.

Y The nely divided solid employed in the bed may have a'particle sizeinthe range from about 100 to about 400 meshand suitably may bejalphaalumina, quartz, Carmullitewhich is a silica-alumina, and the Theamountof hydrogen employed may'be within the range of 6000 to 12,000standard cubic feet per barrel of alkylated aromatic hydrocarbonfeed,`depending upon the hydrogen purity` and operating. severity. While purehydrogen-may be employed, a hydrogen-containing gas such asa catalyticreformertail gas may also be used in suitable amount. Preferred rangesmay Abe from 7000 to 8000 standard cubic feet Aof pure hydrogen per.barrel of `.alltylated aromatic feed, or from 311,000 to 13,000 standardcubic feed of reformeritail gas containing ,75 percent hydrogen perbarrel of alkylated aromatic feed.

' The presentinvention, asstated,is suitably conductedata'temperaturewithinthe. range .from about 1100 to ICC 2 invention maybe any alkylated aromatic hydrocarbon boiling within the range fromabout 200 to about 750"v F., alkylated hydrocarbons such as alkylbenzenes such as illustrated by toluene, xylenes, ethyl benzene,mesitylene, and the like,'and alkyl naphthalenes are illustrativedesirable feed stocks. The alkyl naphthalenes maybe illustrated bymethyl naphthalenes, dimethylnaphthalenes, ethylnaphthalenes,trimethylnaphthalenes, methyl-ethylnaphthalenes and higher molecularweight homologues but other alkylated aromatic hydrocarbons may be used.For example, the present invention may suitably be practiced withalkylated aromatic hydrocarbons in the gasoline and kerosene `boilingranges. f i

The sensing zone employed in the presentinvention to obtain a signalwhich is a function of methane to hydrogen ratio may be any sensing zonewhich will indicate the relative amounts of hydrogen and methane. Forexample, the sensing zone may suitably be a mass spectrometer or may bean indicating or recordingr gasl gravitometer. Other sensing zones suchas a 4gas adsorption chromatographic apparatus, a thermal conductivitycell, or an el'fusiometer 'may be employed.. A signal is obtained fromthe sensing zone which is a function o the methane to hydrogen ratio. i.

The present invention will be further illustrated -by reference to thedrawing in which the single ligure is a llow diagram of a preferredmode.

Referring now to the drawing, a feed aromatic hydrocarbon of the natureillustrated is introduced into the system by line 11 controlled by valve12 and ahydrogenrich gas is introduced intoline 11 by line 2'1controlled by valve 22. `The aromatic hydrocarbon andthe hydro-`gen-rich gas are mixed in line 11 and introduced into a heat exchanger13 wherein the temperature of the total feed is raised to a temperaturewithin the range between about 400 F. and 800 F. The total Vfeed at thistemi perature is withdrawn from theA heat exchanger 13 by line' 14 andmay be introduced thereby into a heater or. furnace 15 and llows throughcoil 16 wherein it is heated to a temperature within the range betweenabout 4700 F. and 900 F. by means 'of heat provided by burners 17.

' The heated feed in a vaporized condition is withdrawn by way of line18 from furnace 15 and introduced into a reaction zone 20. In thereaction zone 20, the preferred reaction temperature of l250 F. to 1350F. 'ismaintained by the highly exothermic reactions of hydrodealkylationand hydrocracking. Alternatively, `the feed aromatic hydrocarbon and thehydrogen-rich gas maybel preheated separately and combined beforebeing:.intro duced at the proper temperatureinto the reaction zone.

-A"lluidized bed 23 is maintained inreaction zone 20 i" of nely dividedcatalytically inert solids of the type mentioned before. The bed 23ismaintained abov'e a reactor grid 24. In reaction zone 20.the reactiontakes place wherein in accordanceiwith the present invention thealkylatedv aromatic hydrocarbons are dealkylated vto form substantiallyonly the desired aromatic hydrocarbons aboutl 1600` F. with a preferredtemperature within the and hydrogen and methane. The products of'the deralkylation reaction are withdrawn from reaction zone 20 by way of line25 and are' quenched in line 25 by means of a quench oil-introducedbyline 26. This' quench Voil may suitablyV bean oil such as the bottomsstream-lev ing fractionator 34 through line 40. vThe quenchedproduct inline 25 at a temperature within therange of about 700 F. to 1000 F. isthen passed through heat exchanger 13 in heat exchange with the feedwhich further reduces the temperature toapproximately 300 F. Thecooled'` The feed. stocksemployedia-the.practicasfffhs Prater.

product `is then introduced by way of line 27 `into`a scrubbingzone 28wherein the quenched and cooled product is `scrubbed with a heavy4 oil,lsuch asrecycled slurry,oil from line 30.11eaving scrubber28,-in'troduc'ed..

to remove any finely divided catalytically inert solids carried overwith the reaction product. The oil and the solids are discharged by wayof line 30 from scrubber 28. The excessl slurry' oil from. line. 30maybe ltered in a lten'zone not shown and introduced into line 31 ahead`of separator 32 in `order to recover all of' the desired product,whilel the catalytically inert solids'recoveredby filtration may bediscarded. 'The reaction products are from zone 20 by line 60 controlledby valve 61. Line 60 withdrawn from scrubber 28 by Way of line 31 into aseparation` zone 32 in'which a separation is made between the gaseousproducts and the liquid products. The liquid products are withdrawn fromseparator 32 by way of line 33 and introduced thereby into a fractionaldistillation zone 34. Fractional distillation tower 34 is shown as asingle fractionaldistillation tower which suitably may include aplurality of fractional distillation towers, each equipped-With internalvapor-liquid contacting means, such asl bell cap trays andthe like,means for inducing reux and means for condensingr and cooling thefractionated products. In short, zone 34 will include all auxiliaryequipment necessarily found in the modern distillation tower.

- In zone 34,. temperature and pressure conditions are adjusted'v byVheating means illustrated by steam coil 35 such4 that light hydrocarbonsare removed from zone 34 by line 36 and the dealkylated-hydroearbons arewithdrawn by lines 37, 38, and 39. Heavier products are discharged'Vbyline 40.

Thegaseous products. from separator 32 arewithdrawn therefrom by line 41and'introduced by line 42 into an absorption zone 43 into which absorberoil is introduced by lline 44 to contact countercurrently the residuegas introduced by line 42. The absorber oil may suitably be a streamfromvfractionator 34 such as one of thefproduct streamsv from lines 37,38, 39, or 40.

The absorption zone 43 is operated under suitable conditions oftemperature and pressure to absorb hydrocarbons such as propane,propylene, butanes, butylenes and heavier hydrocarbons While ethane andlighter hydrocarbons including hydrogen are not absorbed. The enrichedabsorption oil is discharged from zone 43 by line 44a for recovery ofthe absorbed hydrocarbons and for stripping' of the absorber oil forre-use in the process. The enriched absorption oil from line 44a mayconveniently be` introduced into line 33y ahead of fractionator 34wherein it will be stripped for re-'use and the absorbed hydrocarbonsrecovered.

Line 45 controlled by valve 46 connects to line 41 and to a sensingmeans or an analyzer 47 to allow the residue gas in line 41 to passtherethrough and be discharged by way of line 48 controlled by valve 49back into line. 42'.

Provision of analyzer or sensing means 47 allows a portion` of theresidue gas in line 41 to be routed through thefanalyzer 47 and backinto line 42.

The unabsorbed residue gas from absorption zone 43 is dischargedtherefrom by way of line 50 andpmay be discarded or recycled to theprocess as a hydrogen-con taining gas.

Connected to line 50 is line 51 controlled by valve 52 'whichA leads toan analyzer or sensing means 53 of the type described. Line 54lcontrolled by valve 55 connects the analyzer 53 back into line 50 suchthat' the residue gas may be circulated through the analyzer 53.

The analyzers 47 and'` S3 suitably connectby electrical leads 54a, 55a,56, and 57 to valve 22 in line 21, valve 12 in line 11 and to valve 58in line 59.

The loperation of the reaction zone 20 is such that the heated feed' isintroduced by means of line 18 in admixture with hydrogen from line 21into the bed 23 of nely divided catalytically inert solids in reactionzone 20. From time to time the catalytically inert solids' may becomefouled with carbonaceous deposits and itis desiralxleu to replace aportion ofthe catalyticallyinert' solids. To end; a portion' of? the:inert solids-*is withdrawn leads into the zone 20 and connects into anannular section 62 dened by the walls 63.

The inert solids in line 60 are carried to a regeneration zone 64 by wayof line 65 connected thereto into which air is introduced by Way of line66 to support a combustion operation in zone '64 above the grid plate67.

The combustion operationburns olf the' carbonaceous matter from thecatalytically inert solids at a temperature in the range from 900 to1500 F. and a combustion product ue gas is withdrawn from zone 64 byline 68.

The burned off catalytically inert solids are withdrawn from zone 64through a zone 69 of zone 64 defined by an annular Wall 70. Line 71controlled by valve 72 connects into zone 69. Line 71 also connects intoa hopper for catalytically inert solids 73 which is connected to line 76by way of line 74. controlled by valve 75,

In operating the present invention, any withdrawn catalytically inertsolids containing carbonaceous material may be replaced by fresh orregenerated catalytically inert solids from hopper 73 by Way of line 74controlled byvalue 75,. .When catalytically inert solids are added,hydrogen is introduced by line 59 controlled by valve 58 to carry'thecatalytically inert solids through line 76 to thebed 23. Hopper 73 iscapable of being operated at the. pressure ofthe reaetionzone 20l whilecatalytically inert solids are being added.

Hydrogen is admixed Withthe feed stock as has been described during theoperation but1 hydrogen is added to line 76 only when it is desired toadd catalytically inert solids from-hoppen73. r

It is to beemphasized that catalytically inert solids may be withdrawnfromi zone 20 and added to zone 20 only at relatively long intervals ascarbonaceous' deposits accumulate on the catalyticallyr inert solids.The amount withdrawn and the amount added may comprise only about 5% byweight of the amount of catalytically inert solids' in the bed 23. `The'interval of time at which catalytically inert solids are Withdrawn andadded may rangefrom about 1 to 20 days. In short,the withdrawal andaddition of -catalytically, inert solids is only at infrequentintervals. The Withdrawn catalytically inert solids containingcarbonaceous material may be cooled and discarded ratherl than`regenerated if desired.

In accordance withv the present invention formation of carbon and cokein the-reaction zone 20 and in the transfer` line 2S yis controlled andsuppressed bymaintaining a ratio of the :thermodynamic equilibriumconcentration of methane (calculated on the basis of the concentrationof hydrogen present) to the actual concentration of methane intheresidue gas above a Value of about 1.7, under the conditions of reactionzone 20.

In order to illustrate the invention further, hydrodealkylationoperations were conducted on a Vfraction boilingy above` 400 F. ofkerosene sulfur dioxide extract which containedabout 86% of' alkylatedaromatics. Thiskeroseneextract was heated to about 800 F. and introducedinto a reaction' zone containingY a uidized bed of silica sand. Theexothermic heat of reaction inv the reaction zone maintained thetemperature of reaction at about 1300 F. Hydrogen-rich gas wasintroduced with hydrocarbon feed to provide the required amount ofhydrogen. Runs were conducted at 1270" to 1345 F., 600 pounds persquarel inch gauge and at 50 to 60 seconds residence time VWith vfrom6600 to 9800 standard cubic feet of hydrogenper barrel of feed beingemployed. The hydrogen employed contained between about 70 and about 79%H2, the other components being methane and heavier hydrocarbons.'

In these operations, coking was experienced in the reaction zone. In oneof the runs at 1320" F. and 600 pounds per square inch gauge, it wasfound that the concentration of hydrogeninfthe' residue gas was 32.3mole .fatwa-M99 r percent- A'Ihenthermodynamic equilibrium concentrationcorresponding to the actual'hydr'ogen concentration was 45.1 molepercent.= Theratio of the equilibrium methane concentrationto theactualmethane concentration was 0.95. In this run the operation had to beterminated after hours due to coking.-' l

In another run with the same feed stock and 600 pounds persquareinchgauge, the residue gas contained 35.6 mole percentnhydrogenand 44.7 mole percent of methane. The thermodynamic equilibriumconcentration of the 'methanecorresponding `to thehydrogen was 56.5 molepercent.y The ratio of equilibrium methane concentration to the actualmethane concentration was .1.26. This run hadtobeV terminated after 12hours due to :coking.` 1

It has been observed that the only hydrocarbon in the product underconditions existing at the reaction zone outlet which may bethermodynamically stable is methane. In the presence of sufficienthydrogen to make methane thermodynamically stable, the heavierhydrocarbons decompose and result in the formation of methane. In thepresence of smaller quantities of hydrogen than are necessary to makemethane thermodynamically stable, the decomposition reaction results inthe formation of carbon and hydrogen. This carbon deposits on the walls,lines and in the reaction zone and makes the operation inoperable ifallowed to continue. A measure of the ability of hydrogen to preventcoking is the degree of approach of the partial pressure of methaneactually present to the partial pressure of methane that exists inthermodynamic equilibrium to the hydrogen under the conditions existingin the reaction zone. The equilibrium concentration of methanecorresponding to the hydrogen concentration at reaction zone conditionsmay be determined by calculation based on the thermodynamic datapublished by the Carnegie Press for American Petroleum InstituteResearch Project 44, Selected Values of Physical and ThermodynamicProperties of Hydrocarbons and Related Compounds. y

It has been found that, if the ratio of equilibrium methaneconcentration to the actual methane concentration in the reaction zoneis maintained above about 1.7 times the thermodynamic equilibrium ratio,the formation of coke may be suppressed or controlled. This operationmay be effected by controlling the amount of hydrogen added to the feedor by varying the amount of hydrogen with respect to the feed. In short,either increasing or decreasing the hydrogen or increasing or decreasingthe feed aromatic hydrocarbon may allow the formation of carbon in thereaction zone to be controlled.

To illustrate the present invention a number of runs were conducted withthe same sulfur dioxide kerosene extract, employed in previous runs,wherein the ratio was varied in accordance with the present invention.

These operatlons are summarized in the following table:

Table I Run Period, Hours 14-26 26-38 38-50 50-62 Reactor Temperature, F1, 290 1, 290 1, 295 1, 295 Reactor Pressure, p.s.i.g. 600 600 600 600Charge Gas:

S.c.f./bb1. Feed 11, 250 11,510 10, 330 10,090 H2, Mol Percent 76.1 77.5 76. 4 76.1 Residue Gas:

Specific Gravity (Referred to Air 0. 428 0. 430 0. 460 0. 465 H2, MolPercent.. 43. 4 43. 0 38. 3 37. 5 01:14, Mol Percent 37. 4 37. 8 42. 142. 9 Calc. Equil. CH4, Mol Percent.. 97. 7 95. 9 73.8 70. 8 RatioEquil. (BH4/Actual CH4.- 2. 61 2. 54 1. 75 1. 65

It will be seen that during the series of yield periods, the ratio ofthe calculated equilibrium concentration of methane to the actualconcentration decreased continuously during the yield periods. After 62hours, the ratio had dropped to a value of 1.65, and the run wasterminated by coking.

.6 In; anothertrun the concentrationothydrogen and 'methane in ,theIresidue 'gas werel controlled.- 4by varying the. quantity ofrthecharged gas so that the specific grav'- ity, with referenceto ain,of the residue gas remained within the limits of 0.43 to 0.45. Theresults of consecutive yield periods 4for this run are shown in TableIl:

Table llf Run Period, Hours- 9-21 21-57 57-69 'G9-103 ReactorTemperature, F.- 1, 315 1,315 1,320 1,325 Reactor Pressure, p.s.i.g r600 600 600 600 Charge Gas: l

S.c.f./bb1. Feed---- 13,080 11, 770 12, 440 12, 550 H2, Mol Percent y75.2 `76.4 76.3 73.6 Residue Ges:

. Specific Gravity I.

A-ir .436. 0.442 0.432 0. 446 Hq, Mol Percent. -`42. 1 41. 2 42. 7 40. 5CHI, Mol Percent..-- 38. 6 39.4 38.1 40. l Calc. Equll. CHI. MolPercent.. 79. 1 75. 7 78.8 69. 0 Ratio Equil. CB14/Actual CHL.. 2. 05 1.92 2. 07 1. 72

It will be seen from these data that by maintaining the ratio ofequlibrium concentration of methane to the actual concentration aboveabout 1.7 that coking is substantially eliminated and further that theoperation may be controlled by varying the concentrations of hydrogenand methane in the residue gas.

The present invention is quite advantageous and useful in that coking inhydrodealkylation of aromatic hydrocarbons may be suppressed, controlledor entirely eliminated.

The nature and objects of the present invention having been completelydescribed and illustrated, what I wish to claim as new and useful and tosecure by Letters Patent is:

1. A method for controlling and suppressing the formation of coke in athermal dealkylation zone in which an alkylated aromatic hydrocarbonfeed is heated in said dealkylation zone in the presence of hydrogen to4a temperature within the range between about l and about 1600 F. and ata pressure within the range between about 400 and about 1000 pounds persquare inch gauge for a time within the range between about 2 and about120 seconds in the presence of a fluidized bed of catalytically inertfinely divided solids in which a liquid product and a residue gas areproduced which comprises the steps of analyzing said residue gas toobtain a signal which is a function of the methane to hydrogen ratio inthe residue gas, and employing said signal to vary the ratio of hydrogenand alkylated aromatic hydrocarbon feed in said thermal reaction zone toprovide a methane to hydrogen ratio in said residue gas such that theratio of the thermodynamic equilibrium methane concentration to theactual methane concentration is above about 1.7.

2. A method in accordance with claim 1 in which the amount of hydrogenand alkylated aromatic hydrocarbon feed is varied by varying the amountof hydrogen.

3. A method in accordance with claim l in which the amount of hydrogenand alkylated aromatic hydrocarbon feed is varied by varying the amountof alkylated aromatic hydrocarbon.

4. A method for controlling and suppressing the formation of coke in athermal dealkylation zone in which an alkylated aromatic hydrocarbonfeed is heated in said dealkylation zone in the presence of hydrogen toa temperature within the range between about 1100 and about 1600 F. andat a pressure within the range between about 400 and about 1000 poundsper square inch gauge for a time within the range between about 2 andabout 120 seconds in the presence of a liuidized bed of catalyticallyinert finely divided solids in which a liquid product and a residue gasare produced which comprises the steps of owing said residue gas througha sensing zone to obtain a signal which is a function of the methane tohydrogen ratio @in Athe residue gas, 'and employing `said signal such:that .the ratio o'f the thermodynamic equilibrium methane concentrationto the `actual methane Aconcentration ris above about 1.7.. .y A

5. A method in accordance with claim 4 in which the alkylated aromatichydrocarbon boils within the range from about 200 to about 750 F.

6. A method in accordance with claim 4 in which the amount of `hydrogenand alkylated aromatic hydrocarbon feed is varied by varying theamountof hydrogen.

7. A method in accordance with claim 4 in which the amount ofhydrogenand alkylated aromatic hydro l15 2,853,433k

carbon feed is varied by varying the amount of alkylated aromatichydrocarbon. f

8. A method in `accordance'with claim 4 in lwhich the hydrogen ispresent in, 1an amount within the range of labout 6,000 to abouty'12,000 standard ycubic feet per barrel of aromatic hydrocarbon feed.4K l References Cited 1in the file of this 'patent UNITED `STATES PATENTS2,261,498 AKarcher -a ;....r. Nov. 4, 1941 2,414,889 Murphree v Jan. 28,1947 2,738,307 Beckberger Mar. 13, 1956 2,780,661 Hemminger etal. a Feb.5, 1957 Y KeithA Sept. 23, 1958

1. A METHOD FOR CONTROLLING AND SUPPRESSING THE FORMATION OF COKE IN ATHERMAL DEALKYLATION ZONE IN WHICH AN ALKYLATED AROMATIC HYDROCARBONFEED IS HEATED IN SAID DEALKYLATION ZONE IN THE PRESENCE OF HYDROGEN TOA TEMPERATURE WITHIN THE RANGE BETWEEN ABOUT 1100* AND ABOUT 1600*F. ANDAT A PRESSURE WITHIN THE RANGE BETWEEN ABOUT 400 AND ABOUT 1000 POUNDSPER SQUARE INCH GAUGE FOR A TIME WITHIN THE RANGE BETWEEN ABOUT 2 ANDABOUT 120 SECONDS IN THE PRESENCE OF A FLUIDIZED BED OF CATALYTICALLYINERT FINELY DIVED SOLIDS IN WHICH A LIQUID PRODUCT AND A RESIDUE GASARE PRODUCED WHICH COMPRISES THE STEPS OF ANALYZING SAID RESIDUE GAS TOOBTAIN A SIGNAL WHICH IS A FUNCTION OF THE METHANE TO HYDROGEN RATIO INTHE RESIDUE GAS, AND EMPLOYING AND SIGNAL TO VARY THE RATIO OF HYDROGENAND ALKYLATED AROMATIC HYDROCARBON FEED IN SAID THERMAL REACTION ZONE TOPROVIDE A METHANE TO HYDROGEN RATIO IN SAID RESIDUE GAS SUCH THAT THERATIO OF THE THERMODYNAMIC EQUILIBRIUM METHANE CONCENTRATION TO THEACTUAL METHANE CONCENTRATION IS ABOVE ABOUT 1.7.